Production of a fermentation product

ABSTRACT

A process of separating suspended solids from a fermentation liquor by subjecting the liquor to a solids-liquid separation stage, wherein the fermentation liquor is produced in a fermentation process for the production of a fermentation product, which liquor comprises water, lignin and BOD, wherein the solids liquid separation stage is assisted by a treatment system, characterised in that the treatment system comprises either, (i) a cationic polymer having an intrinsic viscosity (IV) of at least 4 dl/g at a dose of above 2 kg/tonne based on dry weight of suspension, or (ii) a cationic polymer having an intrinsic viscosity (IV) of at least 4 dl/g and, (iii) an anionic polymer, and/or (iv) a cationic polymer of intrinsic viscosity of below 4 dl/g and a cationic charge density of at least 3 meq/g and/or (v) inorganic coagulants and/or (vi) charged microparticulate material.

The present invention relates to processes of treating plant derivedmaterial to provide an aqueous liquor containing sugars which are usedin a fermentation process to produce a fermentation product. Inparticular the present invention relates to a process of dewatering afermentation broth residue, produced as a by-product from thedistillation recovery of a fermentation product. Typically the dewateredsolids are dried and used as a solid fuel. The clarified water wouldnormally be returned to watercourses and/or used as wash liquor furtherback in the process.

Typically such fermentation products include for instance ethanol,glycerol, acetone, n-butanol, butanediol, isopropanol, butyric acid,methane, citric acid, fumaric acid, lactic acid, propionic acid,succinic acid, itaconic acid, acetic acid, acetaldehyde,3-hydroxypropionic acid, glyconic acid and tartaric acid and amino acidssuch as L-glutaric acid, L-lysine, L-aspartic acid, L-tryptophan,L-arylglycines or salts of any of these acids.

It is known to treat a biomass with acid in order to hydrolysepolysaccharides to the component sugars that can be used in afermentation process to produce a fermentation product. For instanceU.S. Pat. No. 4,384,897 describes a method of treating biomass materialin which it is subjected to a two stage hydrolysis in whichpolysaccharides that are more easily hydrolysed, such as hemi-celluloseand then in a second stage the material that is more difficult todepolymerise e.g. cellulose, is depolymerised using a more severehydrolytic treatment. The products of the first and second stagesinclude sugar solutions and organic acids, aldehydes. Themonosaccharides are subjected to fermentation to produce ethanol and thebeer resulting from the fermentation may then be subjected torectification to produce ethanol of commercial grade. U.S. Pat. No.4,384,897 sets out to provide improvements in more efficient washing ofsolids, the use of co-current washing or countercurrent washing ofsolids and proposes the use of ferric and or [aluminum]ions asflocculating agents to separate finely dispersed solids resulting fromthe neutralisation of the hydrolysate liquor stream.

It is also known from a National Renewable Energy Laboratory (NREL)report entitled “Lignocellulose Biomass to Ethanol Process Design andEconomics of Co-Current Dilute Acid Prehydrolysis and EnzymaticHydrolysis Current and Future Scenarios”, NREL/IP-580-26157 (July 1999)to treat cellulose as the second polysaccharide by a cellulase enzyme inorder to hydrolyse the cellulose into its component sugars. In one formof this process the solid by-product residue resulting from the firsthydrolysis step and containing cellulose is divided into a main streamand a secondary stream. The main stream is fed directly into thefermentation vessel and the secondary stream is passed to a cellulaseproduction stage, in which fungi are allowed to grow and act upon thecellulose, such that sugars and cellulase are form. The sugars andcellulase are then fed into the fermentation vessel and the cellulaseacts upon the cellulose from the main stream and converts it into thecomponent sugars which in turn can be fermented to produce thefermentation product.

It is known to treat shredded cellulosic material using concentratedacid to provide aqueous solutions of sugars, which can be used in afermentation process. For instance U.S. Pat. No. 4,650,689 discloses aprocess of preparing ethanol from cellulosic material by subjecting thecellulosic material to highly concentrated mineral acid gas such as HClunder pressure, and treatment with hot water to give a liquor containingsugars which can be fermented.

U.S. Pat. No. 5,975,439 describes an automated process for producingethanol by shredding the cellulosic component of municipal solid wasteand mixing this with equal amounts of concentrated sulphuric acid athigh temperature to provide a digested mixture. The aqueous sugarsolution is separated from the solids by a filtration process beforebeing subjected to a fermentation process.

However, in the recovery of the fermentation product from thefermentation broth it is sometimes necessary to continually distil offthe fermentation product in a distillation stage, wherein a stillagestream, comprising residues and by-products is removed.

WO-A-8603514 describes manufacture of ethanol by fermentation and thenextraction of the ethanol from the fermentation broth. The residualfermentation broth liquor contains yeast and dissolved polymericmaterials such as polysaccharides and proteins. An advantage of locatingthe solid liquid separation stage after the distillation stage is thatsome part of the non-separable dissolved protein in the fermentationliquor is transferred into a separable form through coagulation due toheating in the distillation and heat exchange processes.

In a study by Ann C Wilkie et al (Biomass and Bioenergy 19 (2000)63-102, the treatment of ethanol stillage is evaluated. The bacterium,Zymomonas mobilis has been shown to produce higher ethanol yields butthere is difficulty in separating the stillage liquor from the solidmaterial. The study also identifies the difficulty in separatingsuspended solids from sugar crops and cellulosic crops.

In general, the stillage stream or still bottoms resulting from thedistillation processes are subjected to a solids-liquid separation stepto produce a dewatered product which can be dried to produce a dry solidfuel product. The aqueous liquid separated from the solids are eitherreturned to watercourses and/or recycled as wash water used in thewashing of acid treated plant derived material. The stillage stream orstill bottoms are normally high in BOD (Biological Oxygen Demand) and soit is important to ensure that the aqueous liquor is effectivelyclarified and the water produced therefrom is substantially free ofimpurities in order not to poison watercourses and/or when used as washliquor contaminate the substrate that is being washed.

The stillage stream containing precipitated protein based impurities andhigh levels of lignin, which make it difficult to flocculate and effectsolids-liquid separation. It is known from an NREL report entitled“Liquid/Solid Separation” 99-10600/14 (March 2001) to treat postdistillate slurry with a single polymer solution of concentration 0.01to 0.02 wt %, identified as Perc-765, at doses in the range of 0.4 to 1Kg/tonne of dry solids to effect the dewatering of the solids on a beltpress to a final solids content of 26-29 wt %. However, the filtrateclarity is poor, with separation of a dilute feed of concentration 3 to4 wt % producing a filtrate containing solids of 0.25 wt % or greater.It is noted that when operating with a desired feed concentration of11.7 wt %, the ability to flocculate the solids may be impacted by thisdifference and either dilution of the feed, greater mixing intensity,and/or increased polymer dosages may result. Based on the final solidscontent and the filtrate solids content, belt presses were notrecommended for this application. Furthermore, the liquor is normally atan elevated temperature, for instance above 50° C. and can be as high as95° C. or 100° C. At these elevated temperatures it is normally evenharder to adequately flocculate these liquors. It is therefore anobjective to improve the solids-liquid separation.

A process of separating suspended solids from a fermentation liquor bysubjecting the liquor to solids liquid separation stage, wherein thefermentation liquor is produced in a fermentation process for theproduction of a fermentation product, which liquor comprises water,lignin and BOD, wherein the solids-liquid separation stage is assistedby a treatment system, characterised in that the treatment systemcomprises either,

-   -   (i) a cationic polymer having an intrinsic viscosity (IV) of at        least 4 dl/g at a dose of above 2 kg/tonne based on dry weight        of suspension, or    -   (ii) a cationic polymer having an intrinsic viscosity (IV) of at        least 4 dl/g and,    -   (iii) an anionic polymer, and/or    -   (iv) a cationic polymer of intrinsic viscosity of below 4 dl/g        and a cationic charge density of at least 3 meq/g and/or    -   (v) inorganic coagulants and/or    -   (vi) charged microparticulate material.        Intrinsic viscosity is measured using a suspended level        viscometer in 1M NaCl buffered to pH 7.5 at 25° C.

A BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a test rig in part sectional side elevation.

FIG. 2 is a plan view of the rig of FIG. 1.

FIG. 3 is a graph showing the speed of separation at differentdoncentrations of flocculant.

We have found that surprisingly the yield and/or efficiency of theprocess can be improved by effecting a rapid but efficient solids-liquidseparation of the solid residues from an aqueous liquor containing BODand that the liquor can be recycled to the fermentation process. Thetreatment system of the present invention allows a significantlyimproved separation of liquors from the solid residues and by-products.In particular the process induces more effective flocculation and theseparation process is found to be significantly faster. In addition thesolid residues, which contain mainly lignin, resulting from theseparation process have higher cake solids than conventional separationtreatment. Such a solid product would take less time and energy to dryand thus can be for instance used more efficiently as a solid fuel.

Usually the biomass residue comprises in addition to lignin, microbesand residual unconverted cellulose and hemicellulose. Frequently theaqueous liquors will also comprise proteins, polysaccharides, organicand inorganic salts.

It is also important to ensure that very effective separation of liquorfrom the solid by-product is also achieved more rapidly thanconventional treatments.

In one aspect of the present invention the fermentation liquor issubjected to a distillation stage in which the fermentation product isrecovered, wherein the liquor is removed from the distillation stage asa stillage stream and then subjected to the solids-liquid separationstage. Thus in this form of the invention the fermentation liquor isessentially free of the fermentation product when it is subjected to thesolids-liquid separation stage.

Alternatively the fermentation liquor contains the fermentation productwherein the liquor is subjected to the solids-liquid separation stageand then passed to a distillation stage wherein the fermentation productis recovered. Thus in this form of the invention the solids are removedprior to the distillation stage and thus the distillation column and thestillage stream produced therefrom will be substantially free of thesolids.

We have found that the separation process is particularly effective whenthe treatment system comprises a second component in addition to thecationic coagulant. In particular a preferred embodiment employs atreatment system which comprises (i) the cationic coagulant and (ii) ahigh IV cationic polymer of intrinsic viscosity of at least 4 dl/g.

In a treatment system comprising cationic coagulant and high IV polymer,the components may be added simultaneously, either as a pre-mix oralternatively separately. In one preferred form of the invention thecoagulant is added first followed by the addition of high IV polymer.The reverse order of addition is also possible and may be particularlysuited to certain cases.

The cationic coagulant may be a low IV natural, semi-natural orsynthetic cationic polymer which exhibits intrinsic viscosity of below 4dl/g and a cationic charge density of at least 3 meq/g.

Preferably the low IV polymer is selected from the group consisting ofpolyamines, amine/epihalohydrin addition polymers, polymers ofdicyandiamide with formaldehyde, polymers of diallyidimethyl ammoniumchloride (DADMAC), cationic starch and cationic inulin. Polyamines maybe commercially available polyamines, for instance polyethyleneimine(PEI). Cationic starch or cationic inulin may be commercially availableproducts.

Preferred coagulant polymers are addition polymers of formaldehyde withdimethylamine and optionally other amines such as ethylenediamine, forexample commercially available as Magnafloc™ 1597 or polymers offormaldehyde with dicyandiamide, for example commercially available asMagnafloc™ 1797. More preferred low IV polymeric coagulants includepolymers of water-soluble ethylenically unsaturated cationic monomer orblend of monomers at least one cationic, non-ionic or and/or anionicmonomer(s) alone or with other water soluble monomers, provided that thepolymer has a cationicity of at least 3 meq/g. By water-soluble we meanthat the monomer has a solubility of at least 5 g/100 ml at 25° C.Particularly preferred polymers are homopolymers of diallyidimethylammonium chloride or copolymers of diallyldimethylammmonium chloridewith up to 20 mole % acrylamide. Typically such polymers would havemolecular weights of up to 2,000,000 and usually below 1,000,000. Usefulpolymers would ideally exhibit an intrinsic viscosity of below 4 dl/g.

Inorganic coagulants may be any suitable inorganic coagulants, forinstance alum or polyaluminium chloride (PAC).

Anionic polymers may be water-soluble or water-swellable naturalpolymers or their derivatives. These may include starch derivatives,soluble cellulosic polymers, plant gums, marine gums, microbial gums,proteinaceous and polypeptide extracts and synthetic analogues. Theanionic polymer maybe a synthetic polymer that has been formed fromethylenically unsaturated water-soluble monomer or monomer blend. Thesemonomers may include (meth) acrylic acid and its salts, maleic acid andits salts, itaconic acid and its salts and the like.

When the process also involves a cationic coagulant and a high IVcationic polymer, the high IV polymer may be desirably selected fromwater-soluble or water swellable polymers. The polymer may be a naturalpolymer or a synthetic polymer which has been formed from ethylenicallyunsaturated water-soluble monomer or monomer blend. Suitably the high IVpolymer is a flocculating agent selected from the group consisting ofwater soluble or water swellable natural, semi-natural and syntheticpolymers. Natural polymers are desirably chitosan based materials.Preferably the polymer is synthetic and may be formed by polymerisationof at least one cationic, non-ionic or and/or anionic monomer(s) aloneor with other water-soluble monomers.

Preferably high IV polymeric flocculating agents are formed fromethylenically unsaturated water soluble monomers that readily polymeriseto produce high molecular weight polymers. Particularly preferredpolymers include monomers that are selected from the group consisting ofpolyacrylamide, copolymers of acrylamide with (meth) acrylic acid orsalts thereof, copolymers of acrylamide with dialkylaminoalkyl (meth)acrylate or acid addition or quaternary ammonium salts, polymers ofdiallyldimethyl ammonium chloride. The polymers may be linear in thatthey have been prepared substantially in the absence of branching orcross-linking agent. Alternatively the polymers can be branched orcross-linked, for example as in EP-A-202780.

Desirably the coagulant and high IV polymer are added sequentially,preferably employing the coagulant first. In this way the addition ofthe coagulant coagulates the suspended solids and the coagulated solidsare then flocculated by the bridging flocculant. However, in someinstances it may be desirable to add the high IV flocculant firstfollowed by the coagulant. It may also be desirable the coagulant andhigh IV polymer are added simultaneously, preferably as a premix.

In the case where the treatment system employs a premix, the coagulantmay be an inorganic coagulant or the aforementioned low IV polymer.Preferably the pre-mix comprises (i) a low IV cationic polymer ofintrinsic viscosity of below 4 dl/g and a cationic charge density of atleast 3 meq/g and (ii) a high IV cationic polymer of intrinsic viscosityof at least 4 dl/g.

The coagulant is suitably introduced into the aqueous suspension in anysuitable amount in order to effect coagulation of the suspended solids.Usually the dose of coagulant is at least 50 grams per tonne (based ondry weight of biomass residue). The dose of coagulant is usuallysignificantly higher, and can be typically up to 5000 grams per tonne.Usually the amount of coagulant is added in an amount between 500 and3000 grams per tonne, especially around 750 to 2000 grams per tonne.

When the treatment employs a high IV flocculant with the cationiccoagulant, the dose of flocculant is typically at least 50 grams pertonne (based on dry weight of biomass residue). The dose of flocculentis usually significantly higher, and can be typically up to 5000 gramsper tonne. Usually the amount of flocculent is added in an amountbetween 500 and 3000 grams per tonne, especially around 750 to 2000grams per tonne.

In order to ensure that the coagulated and/or flocculated solids areseparated from the liquid medium, the biomass residue is subjected to amechanical dewatering stage during or subsequent to application of thetreatment system. The mechanical dewatering step is ideally selectedfrom at least one of, a centrifuge, a screw press, a filter press, abelt filter press a horizontal belt filter or preferably a pressurefilter.

The liquor separated from the biomass residue comprising sugars and/orcellulose are generally free of unwanted suspended solids and desirablyare recycled into a fermentation process in order to produce afermentation product.

The dewatered biomass residue comprises lignin and thus is generallydifficult to dewater. Generally the dewatered biomass residue issubjected to a drying stage and the dried residue may for instance beused as a solid fuel, a nutrient source for further fermentation or asource of chemicals. The process enables the manufacture of thefermentation product to be made more efficiently. Preferably thefermentation product is selected from the group consisting of ethanol,glycerol, acetone, n-butanol, butanediol, isopropanol, butyric acid,methane, citric acid, fumaric acid, lactic acid, propionic acid,succinic acid, itaconic acid, acetic acid, acetaldehyde,3-hydroxypropionic acid, glyconic acid and tartaric acid and amino acidssuch as L-glutaric acid, L-lysine, L-aspartic acid, L-tryptophan,L-arylglycines or salts of any of these acids.

The following examples illustrate the invention.

EXAMPLE I

Pre-hydrolysis: Milled wood chips steamed with low pressure steam toapproximately 100° C. After steaming concentrated sulphuric acid isdiluted and added to the mixture until the mixture contains 0.52% acidand the solids in the reactor are 22% by weight. The mixture is thensteamed heated to 175° C. for 15 minutes. The mixture is then flashcooled for 15 minutes to remove 6.5% of the acetic acid and 61% of thefurfural and hydroxymethyl furfural.

Separation: The 26% insoluble solids present in the pre-hydrolysedslurry (containing 0.38% sulphuric acid) is treated then separated on afilter press. A method of reducing the toxins remaining in the liquidportion is to wash with (recycled) water. After ion exchange to removeacetic acid, the liquid portion of the hydrolysate is acidified to pH 2by the addition of sulphuric acid. Lime is then added to raise the pH to10 and the liquor is heated to 50° C. The liquid is then adjusted to thefermentation pH of 4.5 for 4 hours allowing gypsum crystals to form forseparation by filtration.

Simultaneous Saccharification and Co-Fermentation (SSCF): Detoxified anddiluted hydrolysed solids are split to cellulase fermentations and SSCFfermenters. The hydrolysate feed stream is 22% soluble and insolublesolids. The portion of hydrolysate split off for Z. mobilis seedproduction is approximately 10%. The portion of hydrolysed solids splitoff for cellulase production is dependent on the cellulase yield on thexylose and cellulose present and the required loading of enzyme in theSSCF. For cellulase production pre-hydrolysed solids-conditionedhydrolysate liquor, recycle water, corn steep liquor (to 1%) andnutrients ((NH₄)₂SO₄, KH₂PO₄, MgSO₄.7H₂O CaCl₂.2H₂O and Tween 80) andcorn oil as an antifoam (0.1% v/v) are combined to give a finalcellulose concentration of 4%. The batch is then run for 160 hours at28° C. to produce cellulase. For SSCF, detoxified hydrolysate slurry(22% total solids) is cooled to 30° C. and added to the fermentertogether with a 10% (v/v) seed inoculum. Addition of corn steep liquorto 0.25% and cellulase to give a final concentration of 15 FPU/g(cellulose) and an initial cellulose concentration of 22%. The SSCFfermentation in which cellulose is converted to fermentable sugars bycellulase and the fermentable sugars converted to ethanol by Z. mobilistakes 7 days.

Distillation: A whole beer containing 5.1% ethanol by weight is fed to adistillation column where the ethanol concentration is reduced to 0.12%by weight, and generating vapour containing 37% by weight ethanol.

Separation: A 200 ml portion of the still bottom stream containing 7.5%suspended solids by weight and 2.5% soluble solids at 85° C. wasflocculated in a Triton mixer set at a speed of 1500 revs per minute andtreated with a 65:35 blend of polymer A (polyDADMAC IV approx 1 dl/g)and polymer B (a cationic polymer active composition 20% acrylamide 80%cationic monomer dimethyl-aminoethyl methacrylate quatemized with methylchloride having an IV of 4 dl/g preferably after shear as described inEP 0202780B) at a dose of 5 kg/tonne dry solids. The flocculatedstillage is allowed one minute of free drainage time. A free drainage of80 ml in 5 seconds is obtained. A sample of the flocculated material wasalso transferred to a piston press. A press cycle of ten minutes is usedwith a maximum pressure of 100 psi. The 5 second filtrate volume was 101ml and the cake solids was 31.4%.

EXAMPLE II

In order to evaluate the separation of liquid from solids in afermentation broth a test procedure was established which will now bedescribed by way of example with reference to the accompanying drawingsin which:

FIG. 1 shows a test rig in part sectional side elevation,

FIG. 2 is a plan view of the rig of FIG. 1 , and

FIG. 3 is a graph showing the speed of separation at differentconcentrations of flocculant.

Referring to the drawings the test rig comprises a vertically orientedopen ended tube 10. the lower end of the tube 10 is disposed just abovefilter paper 12. Contacts 14 are provided on the filter paper which arearranged to supply a signal to a timer 16 to start the timer when liquidspreads to the contacts form the tube 10. A further contact 18 linked tothe timer is arranged to turn the timer off when liquid from the tubereaches the contact 18. Thus the rig measures the time taken for liquidto spread across the filter paper from contact 14 to contact 18. This isknown as Capillary Suction Time (CST) and is a measure of the speed ofseparation of liquid from solid in a sample under test.

A 10 ml sample of fermentation broth was placed in a measuring cylinderand flocculant added. The cylinder was closed and then inverted a numberof times, for example eight times, in order to ensure good distributionof the flocculant in the fermentation broth at low shear. The sample wasthen poured into tube 10 of the test rig and the CST obtained.

The CST, in seconds, of a fermentation broth derived from corn stoverpre-treated with 60 ppm of Polymer 1 was measured at different additionsof cationic flocculant(Polymer 2). The results are shown in the graph ofFIG. 3 which also shows CST for samples with the addition of water inplace of flocculant.

Polymer 1 is a copolymer of 52.5 wt % sodium acrylate and 47.5 wt %acrylamide, IV approx. 11 dl/g

Polymer 2 is a copolymer of 43.5 wt % acrylamide and 56.5 wt % cationicmonomer (dimethylaminoethylacrylate quaternised with methyl chloride),IV approx. 6.5 dl/g.

1. A process of separating suspended solids from a fermentation liquorby subjecting the liquor to a solids-liquid separation stage, whereinthe fermentation liquor is produced in a fermentation process for theproduction of a fermentation product, which liquor comprises water,lignin and BOD, wherein the solids-liquid separation stage comprisesadding to the fermentation liquor, (ii) a cationic polymer having highintrinsic viscosity (IV) of at least 4 dl/g and at least one componentselected from the group consisting of (iii) an anionic polymer, (iv) acationic polymer of low intrinsic viscosity of below 4 dl/g and acationic charge density of at least 3 meq/g, (v) inorganic coagulantsand (vi) charged microparticulate material flocculating the suspendedsolids and lignin in the fermentation liquor and subjecting thefermentation liquor to a mechanical dewatering stage selected from atleast one of, a centrifuge, a screw press, a filter press, a belt filterpress, a horizontal belt filter or a pressure filter to separate theflocculated suspended solids and lignin as cake solids.
 2. A processaccording to claim 1 in which the fermentation liquor is subjected to adistillation stage wherein the fermentation product is recovered,wherein the liquor is removed from the distillation stage as a stillagestream and then subjected to the solids-liquid separation stage.
 3. Aprocess according to claim 1 in which the fermentation liquor containsthe fermentation product wherein the liquor is subjected to thesolids-liquid separation stage and then passed to a distillation stagewherein the fermentation product is recovered.
 4. A process according toclaim 1 in which component- (iv) is added to the fermentation liquor. 5.A process according to claim 1 in which (iv) the low IV polymer isselected from the group consisting of polyamines, amine/epihalohydrinaddition polymers, polymers of dicyandiamide with formaldehyde, polymersof diallyldimethyl ammonium chloride (DADMAC), cationic starch andcationic inulin.
 6. A process according to claim 1 in which theinorganic coagulants are selected from the group consisting of alum andpolyaluminium chloride (PAC).
 7. A process according to claim 1 in whichthe component is (vi) charged microparticulate material.
 8. A processaccording to claim 1 in which the high IV polymer (component (ii)) isselected from water soluble or water-swellable polymers, which polymeris a natural polymer, semi-natural polymer or a synthetic polymer whichhas been formed from ethylenically unsaturated water-soluble monomer ormonomer blend.
 9. A process according to claim 8 in which the high IVpolymer (component (ii)) is either a chitosan based material or apolymer of acrylamide with one or more water soluble cationic monomersselected from dialkylaminoalkyl (meth) acrylates, dialkylaminoalkyl(meth) acrylamides and acid addition salts or quaternary ammonium saltsthereof.
 10. A process according to claim 1 in which the component isselected from the group consisting of (iv) low IV cationic polymer, (v)inorganic coagulants and (vi) charged microparticulate material, and thecomponent and the high IV polymer (component (ii)) are addedsequentially.
 11. A process according to claim 1 in which the componentis selected from the group consisting of (iv) low IV cationic polymer,inorganic coagulants and charged microparticulate material, and thecomponent and the high IV polymer (component (ii)) are addedsimultaneously.
 12. A process according to claim 11 wherein thecomponent is and high IV polymer are a premix comprising- (iv) a low IVcationic polymer of intrinsic viscosity of below 4 dl/g and a cationiccharge density of at least 3 meq/g and (ii) a high IV (component (ii))cationic polymer of intrinsic viscosity of at least 4 dl/g.
 13. Aprocess according to claim 1 in which the dose of coagulant is at least50 grams per tonne (based on dry weight of fermentation liquor).
 14. Aprocess according to claim 1 in which the dose of high IV polymer is atleast 50 grams per tonne (based on dry weight of fermentation liquor).15. A process according to claim 1 in which the mechanical dewateringstage produces a liquid and the liquid produced from the mechanicaldewatering stage is recycled and used as wash water.
 16. A processaccording to claim 1 in which the cake solids are subjected to a dryingstage to provide a dry solid material and in which the dry solidmaterial is used as a solid fuel.
 17. A process according to claim 1 inwhich the fermentation product is selected from the group consisting ofethanol, glycerol, acetone, n-butanol, butanediol, isopropanol, butyricacid, methane, citric acid, fumaric acid, lactic acid, propionic acid,succinic acid, itaconic acid, acetic acid, acetaldehyde and3-hydroxypropionic acid, glyconic acid and tartaric acid, and aminoacids wherein the amino acids are selected from the group consisting ofL-glutaric acid, L-lysine, L-aspartic acid, L-tryptophan, L-arylglycinesand salts of any of these acids.